The Great Barrier Reef is the world's longest coral formation. Situated in the Coral Sea, it stretches for some 1,250 miles (over 2,000 kilometers) between New Guinea and the northeastern coast of Australia. The great reef is actually a series of reefs and coral islands, extending between 10 and 100 miles (15 and 160 kilometers) off the Australian mainland. Over many millions of years, the hundreds of different types of corals have built up "gardens" of unusual and beautiful shapes in varied colors. These attract a wide variety of marine life, including brightly colored fish, sea birds, green turtles, and giant clams and other mollusks. The Great Barrier Reef is an Australian national park and an especially popular tourist attraction.